حسین فالی نژاد

The aim of this work is to determine the dispersion force between two atoms or two neutral molecules. By supposing that atom B can be polarized by vacuum field and the net field at the location of the atom A is the sum of the vacuum field and the field due to oscillating dipole of atom B, using the quadratic stark effect an expression for the energy shift of the ground state of the atom B is introduced (in terms of vacuum state electric field.By considering fields as operators and taking expectation value hn vacuum state, the change in ground state energy is written in terms vacuum electric field correlation function and then related to the imaginary part of the vector potential Green function via fluctuation-dissipation theorem and Cubo's formula. Computing Green function, the interaction energy between the two atoms is obtained in terms of the polarizability and the distance between them. Small and large distances situations are investigated and the consistency with the previous works are shown.